How to Calculate Heat Flow in a Copper and Aluminum Rod Pairing?

[rogerthat4]

Homework Statement

Hello, first question here,

A copper rod and an aluminium rod are in thermal equilibrium with each other. Copper rod = 50cm long and the aluminium rod is 20cm. Radius of pair is 8cm.
Copper end is heated (and maintained) at 80C , other end of pairing is 20C. k of copper is 390 and k aluminium is 210. Calculate the rate of heat flow through the pairing.

Homework Equations

Q/t = kA.(temperature difference, theta)/l

The Attempt at a Solution

Thanks for any help!

 

[mgb_phys]

That's not much of an attempt at a solution.

 

[rogerthat4]

That's not much of an attempt at a solution.

I think this is the answer, not 100%,

delta Q = delta T / SUM ( R )

=> DQ = DT / R1+R2...+...R0

R1 = 1 / k1A , R2 = 1 / k2A ,..., R0 = 1 / k0A

 

[mgb_phys]

You should explain what you have done.
What do you know about the heat flow rate in both materials?

 

[rogerthat4]

You should explain what you have done.
What do you know about the heat flow rate in both materials?

I just need the equation, i am not going to derive everything from first principles, you can see what i have done,

Dt / sum of R where, R is as stated.

I am not William Thomson attempting to experimentally derive with this conclusion, i just have asked for a verification of the above formula.

 

[mgb_phys]

Yes the formula is correct - it's pasted out of wikipedia.
The point of this site is to explain physics and help people understand it.

 

[rogerthat4]

Thanks for your help!

 

[rogerthat4]

Or should it be this,

= DQ = DT/ (L1/k1A + L2/k2A) where L = length of the rod. A = cross sectional area of rod.

i had,

DQ = DT / (1/k1A + 1/k2A)

Is it dependent on the length?